Canada's Conservatives see lead whittled away

* Still points to another minority Conservative government

* Conservatives had big lead after Liberal election threat

* Liberals have pounded away over Afghan detainees

OTTAWA, Dec 17 (Reuters) - The polling lead Canadian Prime Minister Stephen Harper's Conservatives had enjoyed for two months slipped further in December but still points to another minority Conservative government if an election were held now.

A Harris-Decima survey, released by the Canadian Press late on Wednesday, showed the Conservatives at 34 percent and the main opposition Liberal Party at 28 percent.

The Conservatives jumped to as much as 15 points ahead of the Liberals in some polls in October after Liberal leader Michael Ignatieff decided to try to force an election just one year after the last one.

It proved unpopular, particularly as Canada was just emerging from recession, and the Liberals have now backed down.

Parallel with their retreat from the election threat has been a relentless attack on the Conservatives over allegations that Afghan prisoners the Canadian military handed over to Afghan authorities in 2006 and 2007 were subsequently tortured.

An Ekos poll released last week had the Conservatives ahead of the Liberals 35.6 percent to 26.5 percent.

Harris-Decima also had the leftist New Democratic Party at 14 percent and the Greens, which have no seats in Parliament, just behind at 13 percent.

In Quebec, the separatist Bloc Quebecois -- which runs only in the French-speaking province -- kept its commanding lead with 38 percent, followed by the Liberals at 24 percent and the Conservatives at 17 percent.

The telephone survey of 2,012 Canadians was conducted Dec. 3-13. Such a sample size should be accurate to within 2.2 percentage points 19 times out of 20. (Reporting by Randall Palmer; Editing by Eric Beech)